The allocation to elevators of calls given by elevator users is one of the basic tasks of the control of the elevator system. The objective of allocation is to give calls to the elevators to serve in such a way that some desired performance indicator or performance indicator plurality describing the operation of the elevator system would be as good as possible. Commonly used performance indicators are e.g. performance indicators relating to the waiting times of passengers and to energy consumption. In conventional elevator systems a passenger indicates with the up/down pushbuttons that are in the elevator lobby his/her travel direction, and after the elevator car has arrived at the call-giving floor, the passenger moves into the elevator car and in the elevator car gives a so-called car call to the floor to which he/she is going. The call-giving method described above makes it possible that the elevator car serving the call does not need to be decided immediately at the moment the call is given, but instead the control system can repeat the allocation calculation and later decide the elevator car serving the call. In skyscrapers and in other high-rise buildings a so-called destination call system is used to a constantly increasing extent. In a destination call system a passenger gives a destination call to his/her destination floor already with the call-giving device in the elevator lobby, in which case he/she does not need to give a separate car call in the elevator car. Differing from a conventional call-giving system, the elevator car serving a destination call is generally decided immediately when the destination call has been registered.
In elevator technology numerous different calculation methods have been applied for solving an allocation task. Each method, of course, involves a plurality of characteristic parameters that have the purpose of affecting the functioning of the method. In the method e.g. the most suitable parameter plurality can be taken into use in different traffic situations. This is to give the elevator system the opportunity to adapt its operation to be the most suitable with respect to the prevailing traffic situation. The virtue of different allocation options can be compared with a so-called cost function, the aim being to find the minimum value of the cost function and thus to achieve the desired service objectives.
One effective prior-art allocation method for elevators is the use of genetic algorithms especially in systems comprising a number of elevators. The use of genetic algorithms is described in e.g. Finnish patent publication FI112856B.
In the allocation methods known in the art the elevator serving a call is decided but the service sequence (routing) of the calls allocated to elevators is not optimized, but instead so-called collective control is used as the service sequence. In collective control each elevator serves calls in sequence in its run direction. One problem with collective control, however, is that it does not always result in an optimal solution for achieving the desired service objectives in the elevator system.